1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display device, and a liquid crystal display device using the substrate. The invention relates particularly to a color filter substrate for a vertically aligned liquid crystal display device, and a vertically aligned liquid crystal display device using the color filter substrate.
2. Description of the Related Art
In recent years, it has been desired to make an image quality of a thin type display device such as a liquid crystal display higher, decrease a cost thereof, and save electric power therefor. A color filter for the liquid crystal display device is required to have a sufficient color purity, a high contrast, flatness, and other properties to match with a higher image-quality display.
For high image-quality liquid crystal displays, various liquid crystal aligning modes or liquid crystal driving modes such as VA (vertically alignment), HAN (hybrid-aligned nematic), TN (twisted nematic), OCB (optically compensated bend), CPA (continuous pinwheel alignment), and the like, are suggested. As a result, a wide-viewing-angle and high-speed-response display has been put into practical use.
For a liquid crystal display device in the VA mode, which has a structure in which liquid crystals are aligned vertically with a plane of a substrate, such as a glass piece, to give a wide viewing angle and easily operate in a high-speed response, in the HAN mode, which is effective for giving a wide viewing angle, or in other mode, higher-level of flatness for a color filter (evenness of the film thickness thereof, and a decrease in irregularities in the surface of the color filter) and an electrical property, such as a dielectric constant, are desired. Such the high image-quality liquid crystal display pursues, as a main theme, a technique of making a liquid crystal cell thickness (liquid crystal layer thickness) thereof smaller to decrease coloration when the devices are viewed from an oblique direction. For the VA mode, developments of various improved modes have been advanced, and examples of the modes include MVA (multi-domain vertically alignment), PVA (patterned vertically alignment), VAECB (vertically alignment electrically controlled birefringence), VAHAN (vertical alignment hybrid-aligned nematic), and VATN (vertically alignment twisted nematic). A liquid crystal display device in a vertical electric field mode, such as the VA mode, in which a driving voltage is applied along the liquid crystal thickness direction, pursues, as main themes, a higher-speed liquid crystal response, a wide viewing angle technique, and a higher transmittance. About the MVA technique, in order to overcome a problem in that at the time of a liquid-crystal-driving-voltage applying, vertically aligned liquid crystals are unstable (that about liquid crystals initially having vertical alignment to a surface of a substrate, the direction in which the liquid crystals are inclined (brought down) at the time of the voltage applying is not easily settled), disclosed is a technique of creating plural slit-form convex part, forming liquid crystal domains between these slits, and further forming domains having plural aligned directions, thereby ensuring a wide viewing angle. Patent Literature 1 discloses a technique for forming liquid crystal domains using first and second alignment regulating structures (slits).
Patent Literature 2 discloses a technique for forming four liquid crystal domains using light alignment. This patent literature discloses that the following are necessary to ensure a wide viewing angle: conducting alignment treatment plural times, which is related to a strict control of a tilt angle (into 89 degrees); and alignment axes different in angle from each other by 90°, in each domain.
Patent Literatures 3 and 4 each disclose a technique for controlling vertically aligned liquid crystals by effect of an oblique electric field using a transparent electroconductive film (a transparent electrode, a display electrode or a third electrode) of a color filter substrate side, and first and second electrodes of the array substrate side. According to Patent Literature 3, liquid crystals having negative dielectric constant anisotropy are used. According to Patent Literature 4, liquid crystals having positive dielectric constant anisotropy are described. Patent Literature 4 never describes any liquid crystal having the negative dielectric constant anisotropy.
Usually, a liquid crystal display device in the VA mode, the TN mode, or other mode has a basic structure in which liquid crystals are sandwiched between a color filter substrate having a common electrode, and pixel electrodes (for example, a transparent electrode formed into a comb-teeth-form pattern and connected electrically to TFT elements) for driving the liquid crystals and an array substrate. In this structure, a driving voltage is applied between the common electrode on the color filter and the pixel electrodes formed in the array substrate side to drive the liquid crystals. A transparent electroconductive film as the pixel electrodes or the common electrode on a surface of the color filter is usually a thin film of an electroconductive metal oxide, such as ITO (indium tin oxide), IZO (indium zinc oxide), or IGZO (indium gallium zinc oxide).
As a technique disclosing a color filter, for example, blue pixels, green pixels, red pixels or a black matrix, Patent Literature 5 discloses, for example, a technique of forming a transparent electroconductive film above the black matrix and the color pixels, and further laminating an overcoat layer thereon. Patent Literature 6 discloses a technique of forming a cross section of the black matrix into a trapezoidal from. Patent Literature 3 described above describes (in, for example, FIGS. 7 and 9 thereof) a technique of forming a color filter onto a transparent electrode (transparent electroconductive film), which is a technique using plural stripe electrodes and positive dielectric constant anisotropy. Additionally, Patent Literature 7 discloses a technique of forming a color filter onto a transparent electroconductive film.